1. Field of the Invention
The present invention relates to an altitude compensation ignition system for compensating ignition timing of an internal combustion engine having an ignition system, for example, a gasoline engine for an automobile, depending upon variations in altitude or atmospheric pressure.
2. Description of the Prior Art
A conventional internal combustion engine has an ignition timing advance device responsive to revolutions or loads of the engine but in general does not have means for compensating the ignition timing depending upon a higher altitude or a lower atmospheric pressure. Therefore, the engine, used in highlands, considerably reduces its output and increases its fuel consumption resulting in emission of much higher pollutant exhaust gases.
In other words, there have been the centrifugal advance device for compensating the ignition timing responsive to engine revolutions and the vacuum advance device for compensating the timing depending upon engine loads for controlling the ignition timing of an internal combustion engine. In effect, however, these advance devices only meet ignition timing characteristics required at low altitudes.
When an engine is used at higher altitudes or at lower atmospheric pressures, air charging efficiency R during suction strokes decreases owing to the reduced air density and required ignition timing M should therefore be advanced as shown in FIG. 1. More severe knocking occurs with higher altitudes as shown in FIG. 2 wherein a knocking zone in a lower altitude place is shown in Nl and a knocking zone at an altitude of 2,000 meters is in Nh. In recent years, as low octane fuels containing little additions have been widely used to take measures to reduce polluting exhaust gases, knocking zones Nl and Nh are often positioned lower than curves of required (optimum) ignition timing as shown in FIG. 2, so that the ignition timing is frequently unavoidably set at an insufficient advance although the output and fuel consumption of an engine are under worse conditions.
In FIG. 2, Ml indicates the optimum ignition timing at a low altitude, Dl the design ignition timings at a low altitude, Mh the optimum ignition timings at an altitude of 2,000 meters and Dh the design ignition timings at the altitude of 2,000 meters.